Tensions were on the rise on Monday after mystery strikes in Syria reportedly claimed the lives of tens of Iranian pro-regime fighters.

Iran’s supreme leader Ayatollah Ali Khamenei responded to the air assault by threatening retaliation in the event of a military confrontation.

The Iranian leader was quick to play the blame game, accusing the Trump government and new US Secretary of State Mike Pompeo, who was in Jordan on Monday, of “trying to provoke Saudi Arabia and some regional states to confront the Islamic Republic.

“These regional countries should know that if they face the Islamic Republic, they will be definitely defeated," he said.

"Americans are the ones who should leave ... the Middle East, the west of Asia and the Persian Gulf is our home.”

The Syrian semi-official newspaper, Tishreen, claimed the attack was carried out by the US and the UK from their bases in Jordan. On Monday, however, the UK Defence Ministry denied carrying out the attack, while Jordan’s government blasted the “fabricated lies”, adamant that its territory had not been used to carry out strikes.

In Washington, the Pentagon initially declined to comment, while the US Central Command told the Tampa Bay Times “it wasn't aware of any [military] action near Hama”.

Asked later on Monday if the US “assist[ed] with any jamming of radar, or any cyber” in relation to the strikes, Defence Secretary James Mattis said: “We had nothing to do with the strike last night.”

Mattis on strike near Hama last night in Syria: "We had nothing to do with the strike last night." My question was: "Did you assist with any jamming of radar, or any cyber." Strike believed to be carried out by the Israeli warplanes, targeted Iranian weapons stored in Syria.

Social media accounts showed videos of massive explosions and fire rocking the area amid conflicting reports regarding the targets hit, the death toll and the identity of those killed.

Local reports said the base in Hama was home to the regime's 47th Brigade and that Iranian military cadres helping President Bashar Al Assad were present in the area.

Early reports by ISNA (Iranian students news agency) concluded that 18 Iranians were killed. The report was subsequently removed and replaced by a different piece claiming that 40 to 60 Syrians were killed - but made no mention of Iranian casualties.